Purification of gases



June 18, 1940. s. A. LE cRoY PURIFICATION OF GASES Filed oct. 12, 1937 LNWUW Olm In {u} @i i :Q

n vos wv NN (Hows 1 ww IAN Patented June 18, 1940 UNITED STESPURIFIOATION F GASES Sylvester Alton Le Croy, Baton Rouge, La., as-

signer to Standard Oil Development Company, a corporation of DelawareApplication October 12, 1937, Serial No. 168,532

1 Claim.

This invention relates to the purification of gases. It is concernedwith the removal of carbon dioxide from a gaseous hydrogensulfide-carbon dioxide mixture. The invention especially relates to theseparation of carbon dioxide from hydrogen sulfide by means of a calciumhydroxide solution when said hydrogen sulfide is secured by treating aCrude metallic sulfide, containing mixed carbonates as impurities, witha mineral acid.

It is known to commercially prepare hydrogen sulfide by treating crudemetallic sulfide as, for example, sodium hydrosulfide, containing mixedI carbonates as impurities, with a mineral acid. The hydrogen sulfidegas secured in this process contains carbon dioxide which is formed fromthe reaction of the acid on the carbonatos. For most operations, thepresence of carbon dioxide in the hydrogen sulde does not necessarilyimpair the subsequent use of the hydrogen sulfide. However, in otheroperations when the hydrogen sulfide is utilized for certain purposes,as for example in the manufacture of sensitive catalytic material, it isimperative that the carbon dioxide be completely removed in aneconomical manner.

The present invention uses a solution of calcium hydroxide to purify thehydrogen sulfide and remove the undesirable carbon dioxide in a manneras may be readily understood by reference to 5,51 the attached drawingillustrating one modification oi the invention. Concentrated mineralacid is led from the acid storage tank I by means of line 2 into aciddilution tank 3 where the acid may be diluted to the strength desired byintroducing water through line 4. This tank may be suitably equippedwith venting, cooling or refrigerating and agitating means. 'Ihe dilutedacid is then led into an overhead feed tank 5 by means of line d fromwhich tank the acid is led at the desired rate into the hydrogen sulfidegenerator l. The metallic sulfide, containing as impurities mixedcarbonatos, is introduced into the hydrogen sulfide generator 'i fromstorage tank 8 by means of line Q. The evolved hydrogen sulfide,

containing as impurities carbon dioxide, is taken overhead from thehydrogen sulfide generator by means of line II). The spent reactionproducts in the hydrogen sulfide generator 'i are neutralized with analkali solution from tank I! introduced 5b" through line i2. The spentneutralized products are withdrawn by means of line I3.

The hydrogen sulfide-carbon dioxide gaseous mixture is led into thebottom of the scrubbing tower i4 by means of line I0. The gases rises5'5! through the tower encountering a counter-flowing saturated calciumhydroxide solution which hasy previously been saturated with hydrogensulfide. The scrubbed gases are taken overhead by means of line I5 andintroduced into the bottom of scrubbing tower I6 where they flowupwardly and 5 are scrubbed with a countercurrent flowing saturatedcalcium hydroxide solution containing aA suspension of calciumhydroxide, said solution being previously saturated with hydrogensulfide.

The hydrogen sulfide scrubbed gases free from 10 carbon dioxide aretaken overhead by means of line I'I and led to a suitable storage tankor gas holder. The spent calcium hydroxide solutions containing thecarbon dioxide are withdrawn from the bottom of gas scrubbing towers I4and 10 I6 by means of lines I8 and I9 and are led into tank 2@ wherethey may be further treated or discarded. Gas scrubbing towers I4 and I6may contain suitable contacting and distributing means as, for example,bubble plates or contact 20 masses. These towers are also equipped Withrecycling means whereby the calcium hydroxide solutions from the bottomof the towers may be introduced into the calcium hydroxide feed lines 2land 22 through which the `calcium hydroxide 25 solutions are introducedinto the top of the scrubbing towers. The fresh lsaturated calciumhydroxide scrubbing solution containing a suspension of calciumhydroxide is stored in storage tank 23 from which it may be led into thehydro- 30 gen sulfide saturating tanks 24 and 25. The calcium hydroxidesolution led into tank 24 is preferably taken from approximately thecenter of tank 23 by means of line 26. The calcium hydroxide solutioncontained in tank 25 is taken from the 35 bottom of tank 23 by means ofline 2'I and therefore contains a calcium hydroxide suspension. Thecalcium hydroxide solution from tank 24 is used in the first scrubbingtower I4 while the calcium hydroxide solution containing a suspension ofcalcium hydroxide is used in the separate scrubbing tower I6. Thecalcium hydroxide saturated solution contained in tanks 24 and 25 aresaturated with hydrogen sulfide by means of hydrogen sulfide taken fromline Il and introduced into these solutions by means of lines 28 and 29.The excess hydrogen sulfide is returned to line Ii by means of line 30.

The operation may be widely modified with respect to operatingconditions and the flow of gases and liquids. One generator or more maybe employed and the evolved gases treated either in a series or paralleloperation. Although it is preferred to use two scrubbing towers throughwhich the gases flow in series and to introduce into the first scrubbingtower a saturated calcium hydroxide solution and to introduce into thesecond tower a saturated calcium hydroxide solution containing asuspension of calcium hydroxide, this operation may also be widelyvaried. More or less gas scrubbing towers may be used and the gas flowmay be either series or parallel or a combination of these. The calciumhydroxide solution may be of the same strength and need not contain asuspension of calcium hydroxide. Although it is preferable to completelysaturate the saturated calcium hydroxide solutions with hydrogen sulfidebefore introducing these solutions into the scrubbing towers, this isnot absolutely necessary under certain conditions and the calciumhydroxide solution may be introduced directly into the scrubbing towerswithout being saturated with hydrogen sulfide.

The concentration of the sulphuric acid used in the gas generator is inthe range from 30% to 50%, preferably having a concentration of 40%. Theconcentration of calcium hydroxide used is in the range from 0.1% toapproximately a 6.0% suspension, preferably having a concentration of3.0%. The temperature of the calcium hydroxide solution is in the rangeof from 32 F. to 125 F., preferably about 70 F. The desirable pressurein the gas purifying towers is slightly above atmospheric pressurealthough higher pressure may be employed.

A preferred method of purifying the hydrogen sulfide gas from carbondioxide is to first lead the gases into an initial gas scrub-ber throughwhich a relatively weak calcium hydroxide solution having aconcentration of about 0.2% is circulated and then to lead the existgases from this purifier into a subsequent purifier through which arelatively strong calcium hydroxide solution is circulated, preferablyof a concentration of about 3.0%, both solutions being at a temperatureof about '70 F.

One method of conducting the process as applied to the attached drawingis given in the following example:

Example 1 Concentrated sulphuric acid from storage tank l is led intostorage tank 3 by means of line 2 and diluted to approximately 40%concentration. This diluted acid is led into the gas generator l whereit contacts the solution of crude sodium hydrosulfide containing asimpurities mixed carbonates. Evolved hydrogen sulfide and carbon dioxidegases are taken overhead by line l and led into the lower part of towerIll. The spent reaction mixture in the generator 'l' is neutralized witha 5% sodium hydroxide solution from alkali tank ll and is then withdrawnfrom the generator 1 through line i3. The hydrogen sulfide-carbondioxide gaseous mixture led into the lower section of tower I4 iiowsupwardly intimately contacting counter-flowing saturated calciumhydroxide solution of about 0.2% concentration. The scrubbed gas fromtower i4 is then led into the lower section of tower i6 where it iiowsupwardly intimately contacting counterflowing saturated calcium.hydroxide containing a 3% suspension of calcium hydroxide. The hydrogensulde gas free of carbon dioxide is then taken overhead by means of linei7 and led to a suitable gas holder. The scrubbing calcium hydroxidesolutions used in towers i4 and l5 previously saturated with hydrogensulde in saturating tanks 24 and 25 by means of hydrogen sulfide ledfrom line Il.

Ercample 2 650 parts by volume of saturated calcium hydroxide containingapproximately 3.0% of calcium hydroxide as a suspension was saturatedwith hydrogen sulfide. This solution saturated with hydrogen sulfide wasled into 3 scrubbing units connected in series. A mixture of 1500 partsby volume of hydrogen sulfide and 500 parts of carbon dioxide was passedthrough the solutions maintained at a temperature of about 60c F. and atabout atmospheric pressure. Approximately 1500 parts by volume of exitgas was collected which was then passed through a Solution of cadmiumacetate in order to determine the presence or absence of carbon dioxide.The entire volume of the exit gas was absorbed in the cadmium acetatesignifying the complete absence of carbon dioxide in the hydrogensulfide gas evolved from the calcium hydroxide solutions.

In processes where the hydrogen sulfide gases containing carbon dioxideare first led into calcium hydroxide solutions which have not beenpreviously saturated with hydrogen sulfide, the solution will take upboth the carbon dioxide and hydrogen sulfide until a point of saturationis reached with respect to the hydrogen sulfide. At this point.secondary reactions occur and thereafter the hydrogen sulfidequantitatively passes through the hydrogen sulfide solutions and thecarbon dioxide is absorbed. Thus it is within the scope of thisinvention to separate carbon dioxide from a gaseous hydrogensulfide-carbon dioxide mixture with a calcium hydroxide solution whichhas not previously been in contact with or saturated with hydrogensulfide.

A desirable application of the present invention is in the process ofmanufacturing hydrogen from sulphur containing hydrocarbon gases byreacting,T said hydrocarbon gases with steam. In this process thehydrogen sulfide and carbon dioxide are removed from the hydrogen bymeans of scrubbing with substances such as amino alcohols as, forexample, triethanolamine. The amino solution is reacted by driving offthe absorbed carbon dioxide and hydrogen sulfide. Thus these gases couldbe readily scrubbed with calcium hydroxide in accordance with thepresent invention to produce a hydrogen sulfide gas free from carbondioxide which would be suitable for the manufacture of sensitivecatalytic materials.

The invention is not to be limited by any theory or method of operationbut only by the following claim in which it is desired to claim allnovelty in so far as the prior art permits.

I claim:

A continuous process of preparing pure hydrogen sulfide from a gasmixture of hydrogen sulfide and carbon dioxide which comprisescontinuously contacting said gas mixture in an initial countercurrentscrubbing zone with an aqueous 0.2% calcium hydroxide solution saturatedwith hydrogen sulfide, removing the scrubbed gases from the initialscrubbing zone and rre-scrubbing the same in a second countercurrentscrubbing zone with an aqueous 3.0% suspension of calcium hydroxidesaturated with hydrogen sulfide, continuously saturating new portions ofsaid calcium hydroxide solution and suspension. with a part of thehydrogen sulfide purified in the manner described, and employing thecalcium hydroxide solution and suspension thus treated in the scrubbingof further portions f of the said mixture of hydrogen sulfide and

